Deflocculation of pulp stock suspension with pressure pulses

ABSTRACT

THE INVENTION RELATES TO A METHOD AND MEANS FOR DEFLOCCULATING A STOCK SUSPENSION ON A PAPER MACHINE FORMING WIRE BY APPLYING A SUCCESSION OF PRESSURE PULSES IN REVERSELY ALTERNATE DIRECTIONS TO THE SUSPENSION. THESE PULSES ARE PRODUCED BU INDUCING DRAINAGE OF LIQUID FROM THE SUSPENSION IN A SERIES OF SPACED AREAS EXTENDING TRANSVERSELY OF THE WIRE AND CAUSING AT LEAST A PORTION OF THE DRAINED LIQUID TO FLOW BACK INTO CONTACT WITH THE WIRE IN THE ADJOINING SPACE BE%TWEEN THE DRAINAGE AREAS.   D R A W I N G

fdl 30 1971 o. SEPALL.

DEFLOCCULATION OF PULP STOCK SUSPENSION WITH PRESSURE PULSES med Aug. so., 196s m. w m.

United States Patent O U.S. Cl. 162-208 8 Claims ABSTRACT F THE DISCLOSURE The invention relates to a method and means for deiiocculating a stock suspension on a paper machine forming wire by applying a succession of pressure pulses in reversely alternate directions to the suspension. These pulses are produced by inducing drainage of liquid from the suspension in a series of spaced areas extending transversely of the wire and causing at least a portion of the drained liquid to flow back into contact with the wire in the adjoining space between the drainage areas.

CROSS-REFERENCE TO RELATED APPLICATION Copending application Ser. No. 511,425, filed Dec. 3, 1965, and now abandoned, describes a method and apparatus for deiiocculating a stock suspension web based upon a related principle.

BACKGROUND OF THE INVENTION (1) Field of the invention The invention is in the field of treatment of the pulp suspension web While on the forming wire of a paper making machine to prevent occulation of the fibers therein.

(2) Description of the prior art As was pointed out in the aforementioned copending application, it is usually difficult to obtain a uniform distribution of fibers in the sheet being formed on the wire because there is a strong tendency for papermaking fibers to form flocs, that is, clumps of fibers that adhere to each other and separate only with difficulty. As a consequence, the resulting sheet of paper will vary in weight per unit area and is blotchy or mottled in appearance to transmitted light.

The usual manner of improving poor information is to dilute the suspension further but this presents serious problems because of the large quantities of water to be handled.

Another manner of combating fiocculation is described in U.S. Pat. 3,149,026, issued Sept. 15, 1964, wherein jets of air are directed through the wire onto the suspension thereon.

SUMMARY OF THE INVENTION In accordance with the present invention, fiocculation of fibers in the suspension web on the forming wire is substantially reduced by applying a succession of pressure pulses to the web in reversely alternate directions.

These pulses are produced in a very simple manner by inducing drainage of liquid from the suspension in a series of spaced areas extending transversely of the wire and causing the drained liquid from each area to iiow back against the wire in the space between the drainage areas.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partial sectional side elevation of a device in accordance with the invention in operative relation to a forming wire,

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DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1, 2 and 3, 10` is the conventional forming wire of a papermaking machine and 11 the web of stock suspension on one surface of the wire.

In accordance with the invention, a plurality of drainage foils 12 are applied to the opposite or drainside surface of the wire. Foils 12 each comprise an elongated surface extending transversely of the web and wire and from side to said thereof. Foils 12 may be integrally formed on a body member 13 suitably supported in wireengaging relation.

Foils 12 will, of course, induce drainage from the web in conventional manner. However, instead of withdrawing the drained liquid it is entirely or at least partially retained in the spaces between the foils and then forced back into the wire by means of channels 14. In the modification of FIGS. 1, 2 and 3, each channel has a closed bottom wall 1S and closed walls 16 converging from the foil surfaces towards the wall l15. The reverse flow of drained liquid occurs as a result of the converging channel walls and by the pressure created by the induced drainage of the foil (FIG. 2). The result is a succession of pressure pulses applied in alternating direction to the pulp suspension. The energy is dissipated by turbulence in the suspension which provides a deocculation effect.

FIG. 4 shows an alternative arrangement wherein a plurality of foils 17 are provided with intervening channels 18 provided by downwardly converging walls 19. In this instance, however, bottom wall openings 20` in the channels provide outlets for part of the drained liquid into compartments 21 formed by side walls 22 and bottom walls 23. Means may be provided for controlling drainage from different sections as may be desirable. Such means, as shown, comprises a manifold 24 for each of a number of series of compartments 21, each manifold receiving liquid from passages 25 leading from the cornpartments in its series. Liquid may be drained from each manifold by means of an outlet 26 having a valve 27 therein.

The latter feature is of importance in some instances since fiocculating action decreases as the concentration of fibers increases. It is consequently necessary to retain adequate water during deocculation.

In some instances, it may be desirable to add water to enhance the action. If, for instance, the stock is very slow draining, the defiocculator will be less capable of developing a pumping action and suicient additional water may be added to create a layer that can move in and out of the wire.

The geometry of the foils and the intervening channels may vary widely and will be determined in accordance with existing conditions. In general, the shortest spacing between foils and between opposite slopes in the intervening space, is desirable to provide rapid pulsation and to decrease space requirements. On the other hand, the wearing surface of the foil as contacted by the wire must be large enough to provide a useful life in service.

While the device is shown as applied to only one side of a suspension web, it will be apparent that, for instance, in a two-wire former, the device may be applied to both sides of the suspension web.

I claim:

1. Method of deflocculating a stock suspension web on a paper machine forming wire which comprises an uninterrupted succession of pressure pulses in reversely Patented Mar. 30, 1971 l alternate directions to said suspension by engaging the surface of said Wire on which said web is positioned with a plurality of spaced drainage foils extending transversely of said wire in uninterrupted succession to cause drainage solely by each said foil of a confined stream of liquid into a space between a pair of said foils, and by deiecting each said confined stream while in said space back into contact with said Wire for flow back into said suspension web.

2. Method of deflocculating a stock suspension web on a paper machine forming wire as defined in claim 1, including the step of confining each said space to cause the same streams of liquid drained from said suspension web to flow back in substantially equal quantity into said suspension web.

3. Method of deilocculating a stock suspension web on a paper machine forming wire as defined in claim 1, including the step of withdrawing a portion of the liquid in at least some of said streams whereby only a portion of the liquid drained from said web by said foils is flowed back into said web.

4. Method of deocculating a stock suspension web on a paper machine forming wire as defined in claim 3, including the step of varying the quantities of liquid withdrawn from said streams.

5. Apparatus for detiocculating a stock suspension web on a paper machine forming wire which comprises a body member having rigidly fixed thereto a plurality of spaced parallel drainage foils, each said foil having a flat top surface and side walls extending downwardly therefrom, said side Walls of each adjoining pair of said foils being downwardly converging and forming a channel occupying the entire space between the foils 0f the adjoining pair of said foils, each said channel being thereby of gradually 4 reduced cross-sectional area for upward deection of liquid flowing therein.

6. Apparatus for defiocculating a stock suspension web on a paper machine forming wire as defined in claim 5, each said channel having a closed bottom wall joining said side walls for upward deflection of all liquid fiowing therein.

7. Apparatus for defiocculating a stock suspension web 0n a paper machine forming wire as defined in claim 5, each said channel having an opening between said side Iwalls of a pair of said foils for withdrawal of a portion of liquid owing into said channel.

8. Apparatus for deocculating a stock suspension web on a paper machine forming Wire as defined in claim 5, each said channel having an opening between said walls of a pair of said foils, means forming a chamber communicating with each said opening, each said chamber having a valved outlet for withdrawal of a selected portion of liquid therein.

References Cited UNITED STATES PATENTS 2,083,341 `6/1937 Nash i 162-354X 3,149,026 9/1964 Hornbostel, Il'. 162-297X 3,463,700 8/1969 Brewster 162-351X 3,489,644 l/l970 Rhine l62-354X FOREIGN PATENTS 610,708 12/1960 Canada s.. 162--351 HOWARD R. CAINE, Primary Examiner U.S. Cl. X.R. 

